Lighting systems based on LEDs are used on an increasing scale. LEDs have a high efficiency and a long life time. In many lighting systems, LEDs also offer a higher optical efficiency than other light sources. As a consequence, LEDs offer an interesting alternative for the well known light sources such as fluorescent lamps, high intensity discharge lamps or incandescent lamps.
LED light sources are often comprised in a lighting system, wherein the operation of the LED light sources is controlled by control commands. Such control commands include commands for activating the LED light source and commands for stopping the operation of the LED light source, i.e. commands to start generating a LED current and commands to stop generating a LED current, respectively. In the latter case, operation is not stopped by interrupting the connection of the LED light source to the mains supply but by stopping for instance the operation of a converter circuit comprised in the LED light source. In this latter case, the LED light source is said to be in standby mode. In this standby mode, since the mains supply is still connected to the LED light source, the LED light source is still capable to receive further commands and process those commands. At the same time, however, the mains supply may cause a leakage current through parasitic capacitances and (part of) the LED load comprised in the LED light source. This leakage current can cause the LED string to generate a small amount of light resulting in a glow effect that is often undesirable.
Published international patent application WO 2013/132379, commonly assigned herewith to the same applicant, relates to a LED light source allowing that during operation, a current supplying the LEDs can flow through a current control element and also through a first controllable switch that is maintained in the conductive state. In case the LED current supplied to the LED load by the converter is stopped, the LED light source is in a standby state and the first controllable switch is rendered non-conductive. As a result, leakage currents flowing from the mains supply to the LED load via parasitic capacitances are effectively suppressed, so that the LEDs do not generate a small amount of light during the standby state. However, surprisingly, the LED light source described in WO 2013/132379 cited above, may still suffer from undesirable glow effect during operation under certain conditions.
Notably, though such LED light source functions properly in combination with LED boards having a relatively low capacitance and with LED boards having a relatively high capacitance to protective earth, some glow effect may occur when such LED light source is combined with LED boards having a moderate parasitic capacitance.
In the current disclosure, what will be referred to as a LED load may comprise one LED or a plurality of LEDs. When the LED load comprises a plurality of LEDs in a series arrangement, then what will be referred to as an anode of the LED load will be the anode of the first LED in the series arrangement that is to be flowed through with current, and what will be referred to as a cathode of the LED load will be the cathode of the last LED in the series arrangement that is to be flowed through with current. Similarly, when the LED load comprises a plurality of LEDs in a parallel arrangement, with possibly a plurality of parallel branches each comprising a plurality of LED arranged in series, then what will be referred to as an anode of such an arrangement will be the electrical node that is of the same potential as the anodes of the first LEDs of each parallel branch to be flowed through with current, while what will be referred to as a cathode of such an arrangement will be the electrical node that is of the same potential as the cathodes of the last LED in each parallel branch to be flowed through with current. In other words, the anode of the LED load will be considered as the most positive node thereof, while the cathode will be considered as the most negative node.